Yes, you can connect any device with a MIDI Out (drum pads, keyboard, controller, sequencer) to the OT MIDI In.

You would need some kind of workaround (software, MIDI box, intelligent controller keyboard) to do this. You could play sampled chords on a single OT track, although that would not be very flexible.

If your PC setup can be controlled by MIDI, then you can use the Octatrack to play or sequence your VSTi synths.

Personally, I don’t believe that Elektron will soon have an OT Mk2 that incorporates Overbridge, because Elektron does not replace old models of hardware very often.

I don’t have an AR, but by many reports from users it is easier to use than an OT.

The AR synth engine is optimised for drum sounds. There are some nice demonstrations of bass sounds, but overall it should be much easier to make melodic sounds using a synth like the AF. Using samples for melodic sounds, and especially for chords, is generally a little more time-consuming than using a synth.

No-one outside Elektron knows what their roadmap is, except that Overbridge is scheduled to be released in a few months time. However, it seems reasonable to assume that AF, AK, and AR will not have MIDI out from the sequencer enabled.

You can make your own guesses about what updates or new models Elektron will introduce, but the only way to be confident is to decide what to buy based on the existing or pre-announced features.

The sensible question to ask yourself is “what do I need in order to make better music?” What do you think will be better about your music if you have a 2-unit computerless setup? How would an extra hardware unit help you with your DAW setup?

Only then can you check which unit, if any, would be best to buy.